1. Field of the Invention
The present invention relates generally to a multihop relay Broadband Wireless Access (BWA) communication system. More particularly, the present invention relates to an apparatus and a method for a relay station to transmit to a base station information for the transmission of a broadcast message composed by the relay station and for the base station to inform the relay station of transmission region information of the broadcast message.
2. Description of the Related Art
A fourth generation (4G) communication system, which is a next-generation communication system, aims to provide users with services of various Quality of Service (QoS) levels at a data rate of about 100 Mbps. Particularly, present-day 4 G communication systems are advancing in order to guarantee mobility and QoS in Broadband Wireless Access (BWA) communication systems such as Local Area Network (LAN) systems and Metropolitan Area Network (MAN) systems. Representative examples include an Institute of Electrical and Electronics Engineers (IEEE) 802.16d communication system and an IEEE 802.16e communication system.
The IEEE 802.16d communication system and the IEEE 802.16e communication system adopt Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) schemes for physical channels. The IEEE 802.16d communication system considers only the fixed status of a current Subscriber Station (SS), that is, takes into account only a single-cell structure without considering the mobility of the SS. By contrast, the IEEE 802.16e communication system considers the mobility of the terminal. A mobile terminal is referred to herein as a Mobile Station (MS).
FIG. 1 illustrates a simplified structure of the general IEEE 802.16e communication system.
The IEEE 802.16e communication system has a multi-cell structure, that is, covers a cell 100 and a cell 150. The IEEE 802.16e communication system includes a Base Station (BS) 110 which manages the cell 100, a BS 140 which manages the cell 150, and MSs 111, 113, 130, 151, and 153. Between the BSs 110 and the 140 and the MSs 111, 113, 130, 151 and 153, signals are transmitted and received according to the OFDM/OFDMA scheme. Of the MSs 111, 113, 130, 151 and 153, the MS 130 travels within a boundary between the cell 100 and the cell 150, that is, within a handover area. When the MS 130 moves to the cell 150 managed by the BS 140 while transmitting and receiving signals with the BS 110, its serving BS is changed from the BS 110 to the BS 140.
Since the signaling is conducted between the fixed BS and the MS over the direct link as shown in FIG. 1, the IEEE 802.16e communication system can easily establish a radio communication link of high reliability between the BS and the MS. However, because of the fixed BS, the IEEE 802.16e communication system is subject to a low flexibility in the wireless network configuration. Thus, in a radio environment under several changes of traffic distribution or traffic requirement, the IEEE 802.16e communication system hardly provides for an efficient communication service.
To overcome these shortcomings, using a stationary or mobile Relay Station (RS) or the general MSs, multihop relay data transmission can be applied to a general wireless cellular communication system such as IEEE 802.16e communication system. The multihop relay wireless communication system can reconfigure the network by promptly handling the communication environment change and operate the entire radio network more efficiently. For example, the multihop relay wireless communication system can expend the cell service coverage and increase the system capacity. In a bad channel condition between the BS and the MS, the multihop relay wireless communication system can establish a relay path via the RS by installing the RS between the BS and the MS, to thus provide the MS with a better radio channel. Also, by installing the RS in a cell boundary under the hostile communication condition, the multihop relay wireless communication system can provide a high-speed data channel to the MS and expand the cell service coverage area.
Now, a structure of the multihop relay wireless communication system for the service coverage area expansion of the BS is illustrated.
FIG. 2 depicts a simplified structure of a multihop relay broadband wireless communication system for the service coverage expansion of the BS.
The multihop relay wireless communication system of FIG. 2 has a multi-cell structure, that is, it covers a cell 200 and a cell 240. The multihop relay wireless communication system includes a BS 210 which manages the cell 200, a BS 250 which manages the cell 240, MSs 211 and 213 in the coverage area of the cell 200, MSs 221 and 223 managed by the BS 210 but out of the coverage area of the cell 200, an RS 220 which provides multihop relay paths between the BS 210 and the MSs 221 and 223 outside the coverage area 230, MSs 251, 253 and 255 in the coverage area of the cell 240, MSs 261 and 263 managed by the BS 250 but out of the coverage area 270 of the cell 240, and an RS 260 which provides multihop relay paths between the BS 250 and the MS 261 and 263. Between the BSs 210 and 250, the RSs 220 and 260, and the MSs 211, 213, 221, 223, 251, 253, 255, 261 and 263, signals are transmitted and received using the OFDM/OFDMA scheme.
Next, a structure of a multihop relay wireless communication system for the increase of the system capacity is described.
FIG. 3 illustrates a simplified structure of the multihop relay broadband wireless communication system for the increase of the system capacity.
The multihop relay wireless communication system of FIG. 3 includes a BS 310, MSs 311, 313, 321, 323, 331 and 333, and RSs 320 and 330 which provide multihop relay paths between the BS 310 and the MSs 311, 313, 321, 323, 331 and 333. Between the BS 310, the RSs 320 and 330, and the MSs 311, 313, 321, 323, 331 and 333, signals are transmitted and received using the OFDM/OFDMA scheme. The BS 310 manages a cell 300. The MSs 311, 313, 321, 323, 331 and 333 and the RSs 320 and 333 within the coverage of the cell 300 can transmit and receive signals directly to and from the BS 310.
However, some MSs 321, 323, 331 and 333 near the boundary of the cell 300 are subject to a low Signal to Noise Ratio (SNR) of direct links between the BS 310 and the MSs 321, 323, 331 and 333. The RSs 320 and 330 can raise the effective transfer rate of the MSs and increase the system capacity by providing high-speed data transmission paths to the MSs 321, 323, 331 and 333.
In the multihop relay broadband wireless communication system of FIG. 2 or FIG. 3, the RSs 220, 260, 320 and 330 can be infrastructure RSs installed by a service provider and managed by the BSs 210, 250 and 310 which is aware of the existence of the RSs in advance, or client RSs which serve as SSs (or MSs) or RSs in some cases. The RSs 220, 260, 320, 330 can be stationary, nomadic, or mobile like the MS.
The BS in the multihop relay system can schedule the communications with its managing RS and the communications between the RS and the MS. When the BS schedules both of the relay link between the BS and the RS and the access link between the RS and the MS, the scheduling is referred to as centralized scheduling. By contrast, when the RS directly schedules its MSs without the intervention of the BS, the scheduling is referred to as a distributed scheduling.
The RS can compose a broadcast message for its managing MSs by itself. In the centralized scheduling, the RS needs to inform the BS of information required to schedule the transmission of the broadcast message.
In more detail, when the system adopts the centralized scheduling and the RS itself composes the broadcast message, it is necessary to define a signaling process between the BS and the RS to support the transmission of the broadcast message.